The Maryland Department of Health and Mental Hygiene (DHMH), Infectious Disease and Environmental Health Administration is requesting $4,018,636 over five years from the U.S. Department of Health and Human Services, Centers for Disease Control and Prevention (CDC) to implement the National HIV Behavioral Surveillance System (NHBS) in the Baltimore- Towson, Maryland metropolitan area. The NHBS is an anonymous research study which focuses on recruiting three populations at risk for HIV infection: Men who have sex with men (MSM), injection drug users (IDU), and heterosexuals at increased risk for HIV infection (HET). This study will consist of a series of five cross-sectional surveys using the same interview instrument, which will recruit each of the above risk populations (MSM in years 1 and 4, IDU in years 2 and 5, HET in year 3). The proposed sample size is an annual minimum of 500 participants for the MSM and IDU populations and 450 for the HET population. The proposed study will include a detailed questionnaire to gather information on demographics, sexual and drug use behaviors, HIV testing, and utilization of local HIV prevention program services. The questionnaire will be standardized nationally, with the addition of a limited number of questions specific to Baltimore. The study will also offer HIV testing, utilizing both FDA approved HIV diagnostic tests and the Serologic Testing Algorithm for Recent HIV Seroconversion (STARHS) for the identification of recent infections. The sampling and recruitment methodologies will be selected as appropriate for each of the target populations and will be developed in collaboration with the CDC. MSM recruitment will be venue-based. Public venues (e.g., bars, clubs, etc.) in Baltimore City will be randomly sampled and men will be systematically approached for recruitment. IDU and HET recruitment will utilize respondent driven sampling (RDS). Initial IDU and HET participants will be recruited through key community informants and then be trained to recruit additional members of their risk group. Successive waves of IDU/HET recruits will recruit additional IDUs/HETs. Supplemental funding is requested to perform hepatitis B and C testing during all five years, to recruit 200 male to female transgendered participants using RDS during the first year, and to collect additional blood specimens for further HIV testing during the first year. The NHBS will produce valuable information for measuring HIV risk behaviors for planning and targeting HIV prevention activities in Maryland, and for producing national estimates of HIV risk behaviors in high-risk populations in the most affected regions of the country.